A woman votes in the California primary in Sacramento on June 5, 2012. (Rich Pedroncelli/AP)

In 2002, voters in California were asked to approve Proposition 52, which would have allowed people to register and vote on the same day. Backed by Democratic groups and opposed by Republicans, the proposal would have made it much easier to increase the vote from targeted demographics. Your candidate is supported heavily by older voters? Pull up a bus outside a nursing home, pack it full and drive to the polling place. Anyone not already registered could vote within minutes regardless. The proposal failed by a wide margin -- no doubt thanks to the fact that 2002 was an off-year election in which fewer Democrats vote.

Last week, the California Senate passed a measure that would accomplish the same goal in a different way. Mirroring a law on the books in Oregon, voter registration would now be tied to getting a drivers license. Once you've run the gauntlet at the DMV and gotten your license, you'd automatically be registered to vote, unless you opted out.

The vote in the California Senate, like the vote on Prop 52, drew heavy opposition from Republicans. Ostensibly, the concern was about the integrity of the election system, though evidence of in-person voter fraud remains extremely rare.

But there are two very political reasons that would make Republicans oppose the law as well.

Comparing data on the number of drivers licenses in each county in California with the number of people eligible to vote reveals that the two figures are generally the same. Across the state, there are about 1 percent more people with drivers licenses than are eligible to vote -- mostly thanks to the legal driving age being lower.

If you assume that unregistered voters would mirror registered voters in terms of party distribution, automatically registering everyone to vote would increase the number of Democrats, Republicans and third-party or independent voters by about 27 or 28 percent across the board. But that would mean significantly more Democrats would be added to the voting pool in the state, because it's 27-28 percent of a Democratic pool that is already significantly bigger.

(According to the legislation, people would identify their party at the time they are registered, if desired.)

Right there, then, you can see why Republicans would be skeptical. But notice that this includes an assumption which might not be valid -- that unregistered voters would mirror registered voters in terms of party distribution. It's possible -- or probable -- that those who aren't registered to vote are younger and poorer than those who are. There's a correlation between stability and voter registration: Younger people move more and are less likely to own homes, for example, so their voter registration needs to be updated more regularly. And younger and less-wealthy people are also more likely to identify as Democrats. This means that assuming that the increase to each party or group would be the same is probably incorrect.

The move probably wouldn't automatically increase the number of voters. People who get to vote for the first time in California -- that is, 18- and 19-year-olds -- turn out more than people a few years older, likely because of the novelty of the thing.

That novelty probably coexists with having to go through the process of registering, etc.

But even if more newly registered Democrats don't vote organically, the left can force the issue. Consider the example we used at the outset. Republicans also oppose the bill because of the prospect of Democrats driving buses not to senior centers but to areas with high densities of Democratic voters who might not usually turn out. Republicans tend to vote more consistently than Democrats, meaning that it's the left that needs to focus on increasing turnout -- and has developed established systems for that purpose. The process of getting your voters to the polls becomes much easier when you can assume that everyone in an area is registered to vote already. Making turning out Democratic votes easier is not in Republicans' interest.

This is not yet the law, though it seems likely to be soon. The state Assembly needs to consider some amendments to it and then the bill goes to Gov. Jerry Brown (D) for his signature. At which point, the 13-year-old dream of California progressives comes true: More voters and easier turnout. Meaning that perhaps off-year elections won't be disproportionately Republican in the future.